1. Field of the Invention
The present invention relates to a rodless cylinder for transporting workpiece or the like by displacing a slider in accordance with reciprocating motion of a piston.
2. Description of the Related Art
The rodless cylinder has been hitherto used, for example, for transporting a workpiece. The rodless cylinder basically comprises a piston which is inserted into a cylindrical cylinder tube slidably in its axial direction. A plurality of driving magnets are provided on the outer circumferential surface of the piston so that they face to the inner wall of the cylinder tube. On the other hand, a slider is slidably provided outside the cylinder tube so that is surrounds the cylinder tube. Driven magnets are arranged on the inner circumference of the slider so that they oppose to the driving magnets. When a pressure fluid such as compressed air is introduced into the cylinder tube, the piston is displaced in the axial direction in the cylinder tube. Accordingly, the driven magnets and the driving magnets are magnetically attracted to one another, and the slider slides outside the cylinder tube in accordance with the displacement of the piston.
In some cases, the rodless cylinder comprises a guide member which is disposed in parallel to the cylinder tube for guiding the slider.
In such a case, the outer circumference portion of the cylinder tube contacts with the driven magnets in the conventional rodless cylinder described above. Therefore, the sliding resistance is large, and it is feared that a bush for holding the driven magnets or the cylinder tube is worn to give rise to dust or the like. For this reason, a surface treatment is applied to the surface of the cylinder tube to decrease the sliding resistance in some cases. However, such a treatment has caused expensive production cost of the rodless cylinder. If the assembling accuracy is low for the cylinder tube and the guide member, then the sliding resistance is further increased, and it is feared that dust or the like is generated more frequently. Therefore, it is necessary to assemble the rodless cylinder with a high degree of accuracy, causing a problem that the production cost becomes more expensive.